Tuesday, July 24, 2012

About the top of my new guitar amplifier design

This project stopped for years, but the wood case of my new guitar amplifier is ready. The rason of long time delay while I did nothing is that I used my old amplifiers. One is my previous DIY guitar amp have been disasembled, and I have a Carlsbro GLX100 amplifier with Eminence ReadCoat speaker, whats are very good solutions. This is the reason why I don't hurry with my new idea, but now I take apart my old DIY amplifier and the power supply have been moved to the new wood-case.

My old rack mounted amplifier was stereo for guitar, because I using multieffect. I have Boss GT8, where not only the effects have stereo outputs, this is dual guitar effect, where I can use different amplifiers for left and right channels. This is the reason, why I have combo design but with two speakers for stereo solution:

After the wood case, I have metal cases for electronic circuits:

This is the back of the wood case:

....now without the middle slat because I need space to fix the speakers.

The power supply built to the bottom of wood-case. I know that all other industrial solution have same case with other circuits on the top, but now I have more space on the top for amplifiers and equalizers. I think the larger distance between transformer and circuits have benefits:

The design of wood case was realy good, I made model of paper, and got to the professional carpenter, who manufactured and assembled:

The bottom of this amplifier is done, this is the power supply. From the power supply the required voltages wired to the top of amplifier case:

Here I have +/- 40V for poweramps, +/-18V for preamps, +24V for LED-s relays, and coolers.

But the most important question is what I have on the top

Because the power supply built to the bottom, I have more space on the top. The power of toroid transformer is 1200VA. I want to place guitar preamplifiers and amplifier (stereo for multieffect), and one more stereo poweramp for additional cabinets for vocal or keyboards. I need parametric equalizer, if I have enough space on the top-case, separated for left and right channels. I need audio mixer with mic preamps for vocal or another audio sources with headphone and line outputs.

But the most important question is, what will be the power amplifier on the top case. On this time, I want to build some digital class-D poweramp maybe for vocal only not for guitar. I have PWM power bridges, what is 1x315W, and I have 2x210W TAS chips:

1x350W with TAS5261 is would be enough for guitar, but this power available for 4 Ohm only. The guitar speakers are 8 or 16 Ohms. On 8 Ohm this chip have 125W output power. Now I think, for guitar (where the speaker is 8 Ohm) I will use bridged TDA7293 chips, where I got 200-220W for 8 Ohm speakers. This chip is very popular on guitar amplifier market, Marshall, Carlsbro using this solution. And for example the Crate Powerblock is PWM poweramp.

Because the vocal or additional guitar speakers have less than 8 Ohm impedance, the PWM chip is good solution. The benefit of PWM chip is the very high efficiency. But the disadvantage is the very small size of chip, TAS5261 have digital PWM inputs only, so I need PWM modulator like TAS5028 for example. TAS5028 is more small than TAS5261, so more harder to build the PCB. Finally the PWM modulators have digital inputs, so I need A/D converter for analog input devices.

I'm not sure that I can build complex design with these very small chips. The another detriment is that the PWM modulator and the A/D converter need 3.3V only, what is used for DVD players orfor computer soundcards. I don't think that the vocal or guitar amplifier design is same as like the home theater systems. The power stage of this idea need only non-symmetrical power voltage, +50V. I have +/-40V for TDA bridged solution, what is much better. I can bridged the TDA chips, but I can't bridge TAS power chips, because this is already internally bridged. At he moment I think the bridged TDA circuits are better and easier to build for guitar and vocal.

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